1. Field of the Invention
The present invention relates, generally, to a technique for controlling the RF output of a magnetron of a type employing a pulse-forming network to generate output pulses and, more particularly, to a closed-loop control system for controlling peak current through the magnetron using a peak current sense in a feedback loop.
2. Description of the Related Art
The use of magnetrons in radar systems is generally well known. Such radar systems are extensively used in military applications for detecting aircraft, projectiles, and the like. Magnetron-based radar systems are also routinely employed in weather systems to detect rain clouds, turbulence, and the like.
Presently known magnetrons typically comprise a diode encased in a vacuum tube. The diode essentially comprises a cathode and an anode, wherein a current source is fed to the cathode plate by a compatible current source. A pulse-forming network (PFN) may be utilized to condition a transmit pulse produced by the magnetron.
A PFN typically includes a group of coupled inductors and individual capacitors whose characteristic impedance is approximately matched to the static impedance of the magnetron. The resonant frequency of each LC section in the pulse-forming network and the number of such LC sections determine the pulse width of the RF pulse emitted by the magnetron. As a general rule, the ripple associated with the output pulse may be minimized and the squareness of the pulse enhanced by adding a larger number of LC sections to the PFN.
It is known that magnetron performance drifts as the magnetron ages. This is believed to be due in part to changes in the static and dynamic impedance of the magnetron with age. In addition temperature and other environmental factors can influence the performance of a magnetron. Attempts to control magnetron operation within its optimum operating range have met with limited success. This is due in part to the fact that although it may be possible to control magnetron voltage, the sensitivity of the magnetron output power to the magnetron voltage may be undesirably low. Although the magnetron output power is relatively sensitive to changes in the magnetron current, control of magnetron current has been difficult to achieve in prior art systems.
One known method for controlling magnetron current is to monitor magnetron power output and to manually adjust the magnetron current in the factory or a service center. Unfortunately, this process is time consuming, cumbersome, and expensive to perform.
Accordingly, a need exists for a magnetron current control configuration that overcomes the shortcomings of the prior art.